A. Field of the Invention
The device of the present invention generally relates to molded case circuit breakers and, more particularly, to an improved arc gas external venting system for molded case circuit breakers.
B. Description of the Prior Art
Circuit breakers and, more particularly molded case circuit breakers are old and well known in the prior art. Examples of such devices are disclosed in U.S. Pat. Nos. 2,186,251; 2,492,009; 3,239,638; 3,525,959; 3,590,325; 3,614,685; 3,775,713; 3,783,423; 3,805,199; 3,815,059; 3,863,042; 3,959,695; 4,077,025; 4,166,205; 4,257,403; and 4,295,025. In general, prior art molded case circuit breakers have been provided with movable contact arrangements and operating mechanisms designed to provide protection for an electrical circuit or system against electrical faults, specifically, electrical overload conditions, low level short circuit of fault current conditions, and, in some cases, high level short circuit or fault current conditions. Prior art devices have utilized an operating mechanism having a trip mechanism for controlling the movement of an over-center toggle mechanism to separate a pair of electrical contacts upon an overload conditions or upon a short circuit or fault current condition. Such trip mechanisms have included a bimetal movable in response to an overload condition to rotate a trip bar to open a pair of electrical circuit breaker contacts. Such prior art devices have also utilized an armature movable in response to the flow of short circuit or fault current to similarly rotate the trip bar to cause the pair of contacts to separate. Some prior art devices have included an opening in the molded case for venting or exhausting arc gases that result from electrical arcs formed between separating electrical contacts upon an overload of fault current condition. The amount of venting may be critical since too little venting can result in explosion or severe damage to the case and too much venting can cause external flashover. These venting problems are particularly critical in physically small circuit breakers with high interrupting capacities. An additional problem is that foreign material or environmental contaminants can enter the circuit breaker through the opening for venting.
While many prior art devices have provided adequate protection against fault conditions in an electrical circuit, a need exists for dimensionally small molded case circuit breakers capable of fast, effective and reliable operation and, more specifically, for components thereof that provide the necessary external venting of arc gases while preventing the ingress of environmental contaminants.